Prosthesis suspension liner sealing cap and prosthesis suspension system

ABSTRACT

A prosthesis suspension system comprises a socket for receiving a residual limb, a locking liner having a locking pin for attaching the liner to the socket and a sealing cap disposed between the locking line and the socket. The system further comprises a gap between a skirt of the sealing cap and an interior wall of the socket in which the skirt of the sealing cap is able to move between first and second positions.

This application is a U.S. national-stage application, under 35 U.S.C. §371, of PCT International Patent Application No. PCT/GB2017/052863,filed on Sep. 25, 2017, which claims priority from Application No.1616241.4, filed on Sep. 23, 2016 in the United Kingdom. The entirecontents of these applications are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a prosthesis suspension system and aliner sealing cap for such a system. In particular, the presentinvention relates to a sealing cap for a porous suspension liner formingpart of a reduced pressure lower limb prosthesis suspension system.

BACKGROUND TO THE INVENTION AND PRIOR ART

A prosthesis can be attached to a residual limb in the following manner.A hollow hard socket is custom made to accommodate the shape of theresidual limb. The socket includes means for attaching the prosthesis tothe socket. Before inserting the residual limb into the socket a softflexible liner is typically donned on the residual limb to serve as aninterface between the residual limb and the socket. The liner istypically made from an air impermeable material such as silicone.

There are two types of suspension liners, namely locking and non-locking(often referred to as cushion) liners. In addition to performing acushioning function, locking liners also provide a mechanism forconveniently securing the liner to a socket. To achieve this, lockingliners include an umbrella at their distal end. The umbrella is eitherattached to a distal end of the liner or is partially or fully embeddedwithin the material of the liner. Extending distally from the umbrellais a boss. The boss includes an internally threaded bore for receiving apin. Once in place the pin is fed through a corresponding hole in asocket and locked thereto. In this way the socket is firmly attached tothe liner by means of the pin. An example of such a locking liner isdescribed in WO 95/31160.

An intimate fit is required between the residual limb, the liner and thesocket. This close fit is required to prevent relative motion betweenthe socket and liner and the residual limb, to prevent irritation of theskin and other soft tissue of the residual limb. The intimate fit betterdistributes forces on the residual limb when weight is applied to theprosthesis via the socket. For a lower limb prosthesis, this will occurwhen the prosthesis is in contact with ground, for example when standingand during the stance phase of the gait cycle.

Since the residual limb is surrounded by the liner, when sweat issecreted by the residual limb it is captured within the liner.Furthermore, since the amputee must expend a heightened effort in theresidual limb, the limb is prone to produce increased volumes of sweat.When sweat is secreted onto the skin it can act as a lubricant andreduce adhesion of the limb to the liner. This reduced adhesion leads toa number of problems, such as relative movement between the residual andprosthetic limbs, reduced control and proprioception, increased energyexpenditure leading to further sweating and fatigue, and chafing. Themoist and warm environment resulting from the build-up of sweat withinthe liner also provides an ideal breeding ground for pathogens.

To address this problem liners have been developed which allow removalof sweat, air and other fluids from the liner-residual limb interface,typically using air expulsion arrangements. Air expulsion achieved as aresult of the intimate fit, typically via a one-way valve, is used tocontribute to the formation of a reduced pressure/(partial) vacuumbetween the liner and the socket so that the prosthesis remainssuspended from the residual limb. For a lower limb prosthesis this willoccur during the swing phase of the gait cycle, when the limb is not incontact with the ground. Hence, the presence of a low pressure/vacuumbetween the socket and the residual limb-liner combination is adesirable feature of such prostheses.

A number of methods have been used to maintain a reduced pressure withinthe socket during the swing phase. For example, our patent applicationpublished as GB-A-2486817 describes a vacuum assisted suspension devicefor a prosthesis comprising an air impermeable socket shaped to receivea limb portion. The socket has a peripheral edge and includes anevacuation port and a non-return valve associated with the evacuationport. The evacuation port and return valve are arranged to maintain avacuum between the socket and the limb portion when the latter isreceived by the socket. The device includes a sleeve which spans theperipheral edge of the socket and the limb portion. When air isevacuated/expelled from the socket via the evacuation port the sleeveacts as a seal.

As a further example, our patent application published as EP-A-2254526describes a vacuum-assisted liner system for the socket of a limbprosthesis which secures the prosthesis to a residual body portion. Thesystem includes a flexible liner made of an impermeable material, atleast a distal part of the liner being porous to allow the transport ofair and fluid directly away from the residual body portion to the outersurface of the liner. A fabric distribution layer is located over theliner and between the liner and the socket to allow transmission of suchextracted air and fluid laterally over the liner to an evacuation portin the socket.

There are other known methods of sealing the cavity between the exteriorof the suspension liner and the interior of the socket. For example theliner may include peripheral seals which bear on the interior wall ofthe socket to form an airtight seals. US-A1-2011/0264239 describes asuspension liner sleeve having an elongate, generally conical body. Theliner sleeve includes a plurality of resilient seal elements protrudingradially from the liner sleeve outer surface. A pair of adjacent annularrecesses may be located above and below each of the seal elements. Whenthe limb and liner are inserted into the socket the seal deforms againstthe force exerted by the socket into its associated annular recess andseals against the interior of the socket. A number of alternate sealdesigns are described in that document. Other prior art publicationsinclude U.S. Pat. Nos. 6,726,726, 6,645,253, WO-A-01/070147 andWO-A-02/067825.

US-A-2004/0243251 describes a prosthetic socket having an aperture atits distal end fitted with a seal that is configured in such a way thata tension applied to the said prosthetic socket produces aself-generating force at the seal as a result of the atmosphericexternal pressure increasing the sealing action provided by the sealinglip. The seal may be affixed to the prosthetic socket and/or to a liner,the sealing edge always being radially nearer the aperture to be sealedthan is the root of the sealing lip.

WO-A-2014/205403 describes a moisture management liner device for aprosthetic socket which may include an elongate, cup-shaped, elastomericmember and multiple fluid transport strips. The elastomeric member mayinclude a first material and may extend from an open proximal end to asubstantially closed distal end.

US-A-2012/109336 describes a prosthesis suspension assembly comprising:a prosthetic socket having an open proximal end and a closed distal endand an interior surface, an interface or liner for receiving theresidual limb and fittingly received in the socket, a distal outersurface of the liner comprising a porous or continuously cavitated,compressible material and a proximal outer surface comprising anelastomeric material, a suspension sleeve which seals against theproximal outer surface of the liner and a proximal outer surface of thesocket, and a locking pin connected to a distal end of the liner andlockingly retained in a hole in the distal end of the socket andincluding an air passage therethrough with a one-way valve therein forpermitting the exit of air from an interstitial volume occupied buy saidcompressible material to atmosphere upon ambulation.

A common feature of some of the vacuum suspension systems described inthe above patent publications is that the liner used in those systems isa cushion liner. Since a cushion liner and a socket into which it isinserted are closed at their distal end and open only at their proximalend, in order to suspend the socket and prosthetic limb from theresidual limb it is only necessary to provide an airtight seal at theproximal mouth of the socket and liner, typically by overlapping thejoin between the residual limb, liner and socket with a sleeve. Incontrast, when a locking liner is used the pin of the liner extendsthrough the distal end of the socket. Since the distal seal of thesocket is compromised by the pin passing through it, where a lockingliner is used with a reduced pressure suspension system the airtightseal is achieved between the liner and the residual limb. Consequentlyany perforations in the liner will allow the passage of air between theliner and limb and compromise the suspension of the prosthetic limb fromthe residual limb. For this reason, there is technical prejudice againstperforating locking liners, particularly at their distal end.

The present invention provides an improved reduced pressure prosthesissuspension system.

SUMMARY OF INVENTION

According to a first aspect of the invention, there is provided asealing cap for a porous liner, the sealing cap comprising: a firstportion comprising means for locating the sealing cap on a distal end ofa said liner; a second portion which is resiliently deformable andmovable between, a first position where the second portion is adapted toabut a corresponding portion of the said liner, and a second positionwhere the second portion is adapted to be spaced from said correspondingportion of the said liner.

The means for locating the sealing cap on a distal end of the said linermay comprise means for preventing lateral movement of the sealing caprelative to the distal end of the said liner.

The means for locating the sealing cap on a distal end of the said linermay comprise a protrusion on one of the said liner and sealing cap and acooperating recess on the other.

The said liner may comprise a boss and the means for locating thesealing cap on a distal end of the said liner may comprise a cooperatingrecess in the sealing cap.

The said liner may be a locking liner comprising a bore, the sealing capcomprising an aperture adapted to be in communication with the said boreand the means for locating the sealing cap on a distal end of the saidlocking liner may be a locking pin which is adapted to be fed throughthe aperture into the bore.

The second portion may be a skirt which may have a frusto-conical shape.

The first portion may comprise a frusto-conical part between the meansfor locating the sealing cap on a distal end of a said liner and theskirt.

The frusto-conical part of the first portion may have a thickness lessthan a thickness of the skirt.

According to a further aspect of the invention there is provided aprosthesis suspension system, comprising: a socket for receiving aresidual limb and including mounting means for being mounted to aprosthetic limb; a liner having attachment means for attaching the linerto the socket; and a sealing cap as defined in any one of the precedingclaims, wherein the sealing cap is adapted to be disposed between thelocking liner and socket, the system further comprising a gap betweenthe skirt of the sealing cap and an interior wall of the socket in whichthe second portion of the sealing cap is able to move between its firstand second positions.

The attachment means for attaching the liner to the socket may be one ormore of a locking pin, a vacuum source, a seal between the liner and thesocket and a sleeve for sealing a proximal edge of the socket. Thesocket may have an expulsion port.

The liner may be perforated at its distal end where it is in contactwith the skirt.

The liner may have an outer wicking layer and the distal end of theliner may be perforated where it is in contact with the first portion ofthe sealing cap.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, andwith reference to the accompanying drawings in which:

FIG. 1 is an exploded perspective view of a perforated liner and sealingcap forming part of the reduced pressure prosthesis suspension system inaccordance with an embodiment of the invention;

FIG. 2 is a sectional view of the sealing cap shown in FIG. 1 inaccordance with an embodiment of the invention;

FIG. 3 is a sectional view of the perforated liner and sealing cap shownin FIG. 1 when the sealing cap is disposed on the liner; and

FIGS. 4A and 4B are partial sectional views of the prosthesis suspensionsystem in the region of the sealing cap when a skirt thereof is in afirst and second position respectively.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a distal portion of aperforated locking liner 1 and sealing cap 3 forming part of a reducedpressure prosthesis suspension system in accordance with an embodimentof the invention. As is renowned in the art, in addition to the liner 1and cap 3 shown in FIG. 1, the system further includes a socket andlocking pin, not shown in FIG. 1.

The perforated liner 1 comprises a flexible silicone body coveredcircumferentially with a fabric layer 5. An end cap 7 is fixed to adistal end 9 of the liner 1. An outer face 11 of the end cap 7 has afrusto-conical portion 13 with a boss 15 protruding distally from itscentre 17. The boss 15 has a threaded bore 19 at its centre. The distalend 9 of the liner 1 is perforated, the perforations 23 passing throughthe end cap 7 and the silicone body. The density of the perforations 23is around 5-10 perforations per square cm. The density of perforations23 may be reduced where the perforations 23 pass through the body of aninternal umbrella, so as not to adversely compromise the structuralrigidity of the umbrella. Conversely, the density of perforations 23 maybe greater where the perforations pass through fenestrations (throughholes) in the umbrella. Furthermore, the number of perforations 23 persquare cm may vary depending on mechanical properties (such as theresilience) of the material from which the liner 1 is made. Theperforations 23 in use allow passage of air and sweat from the interiorof the liner 1 to its exterior over an extended area of the residuallimb. Other than the perforations 23 passing through the end cap 7 ofthe liner 1, the liner 1 is impermeable in a region immediately proximalto the end cap 7 so that the only permeable zone of a distal region ofthe liner 1 is through the end cap 7. The impermeable region of the line1 may extend to a proximal rim of the liner or may extend around 10 cmin that direction, with a perforated or otherwise permeable regionextending proximally to the impermeable region.

The sealing cap 3 has a similar overall shape to the end cap 7 of theliner, having a generally frusto-conical portion 25 with a boss 27extending from its centre 29. The boss 27 has a smooth walled(unthreaded) central through bore 31. The sealing cap 3 is made fromsilicone- and may be made from other resiliently deformable materialsuch as urethane, rubber or other materials having a hardness within theShore A scale. A preferred feature of the material of the sealing cap 3is that it is resistant to the slightly acidic properties ofperspiration.

The sealing cap 3 is shown in section in FIG. 2 and in FIG. 3 thesealing cap 3 is shown mounted on the distal end 9 of the liner 1. Ascan be seen in these Figures, the sealing cap 3 has a similar shape tothe outer face 11 of the end cap 7. In particular the interior surface33 of the sealing cap 3 is shaped to match the corresponding outer face11 of the end cap 7. The interior surface 33 of the sealing cap 3includes a boss recess 28 on the interior of the boss 27 which is shapedto fit over the boss 15 of the liner 1 such that the engagement of theboss 15 in the boss recess 28 locates the sealing cap 3 on the liner 1by preventing relative lateral (left-right and in and out of the page asshown in the Figures) movement of these parts 1, 3.

The outer face 35 of the sealing cap 3 includes a plurality ofconcentric grooves or marks 37. The sole function of these grooves 37 isto assist cutting the sealing cap 3 to a required diameter. Sincelocking liners are supplied in different sizes the sealing cap 3 ismanufactured having a diameter equal to or greater than the diameter ofthe largest supplied locking liner end cap and the grooves 37 are usedas guides to aid a prosthetist or prosthetic technician in reducing thediameter of the sealing cap 3 to a suitable size. Alternatively sealingcaps 3 without grooves or marks 37 and having different diameters may bemanufactured, for example corresponding to the size of common liners.

The thickness of the sealing cap 3 differs between an innercircumferential band 39I of the frusto-conical portion 25 of the sealingcap 3 and an outer circumferential band 39O thereof. Whilst the interiorsurface 33F of the frusto-conical portion 25 of the sealing cap 3 has agenerally frusto-conical shape, a step 41 is formed in the outer face 35of the sealing cap 3 as the thickness of the sealing cap 3 transitionsfrom a thickness t_(i) of the inner circumferential band 39I of thefrusto-conical portion 25 and a thickness t_(O) of the outercircumferential band 39O of the frusto-conical portion 25, wheret_(i)>t_(O). The reduced thickness t_(O) of the outer circumferentialband 39O, referred to herein as the ‘skirt’ of the sealing cap 3, makesthis portion more flexible than the inner circumferential band 39I ofthe frusto-conical portion 25. It will be apparent to the skilled personthat whilst the ‘full’ thickness t_(i) inner circumferential band 39I ofthe frusto-conical portion 25 is the load bearing portion, bearing theweight of the amputee, the reduced thickness t_(O) of the outercircumferential band 39O of the frusto-conical portion 25 allows thisportion of the sealing cap 3 to move when the liner 1 and sealing cap 3are within a socket, as explained below. For convenience we hereindefine the functional parts of the sealing cap 3 as the boss 27 and theinner circumferential band 39I of the frusto-conical portion 25 togetherforming a first portion of the sealing cap 3 which, in use, is heldagainst the end cap 7 of the liner 1 and the outer circumferential band39O of the frusto-conical portion 25 of the sealing cap 3 can be definedas a second portion.

As is known in the art, a first step of producing a socket for aresiduum is forming a cast around the residuum when a liner is donnedthereon. When casting a socket for the liner 1 described above it isnecessary to apply a casting gasket over the reduced thickness skirt 39Oso that when the final socket is applied to the liner 1 and sealing cap3 a cavity will exist between the skirt 39O of the sealing cap 3 andsocket, as described below with reference to FIGS. 4A and 4B.

FIGS. 4A and 4B are close-up sectional views of the prosthesissuspension system comprising the sealing cap 3 and liner 1 in a socket43, with the skirt 39O of the sealing cap 3 in alternative positions. Asdescribed in the Background to the Invention above, the socket 43 ismade of a hard impermeable material that is shaped to fit a residuallimb 45.

In FIG. 4A, the liner 1 has been donned on the residual limb 45 of anamputee, the sealing cap 3 has been positioned over the end cap 7 of theliner 1, and the resulting combination has been inserted into the socket43. The liner 1 includes a locking pin 47 which is screwed into thethreaded bore 19 of the boss 15 of the liner, through the bore 31 of theboss 27 of the sealing cap 3 and through an aperture 49 in the socket43, forming an airtight seal between the cap 3, boss 15 and distal end 9of the liner 1. As can be seen in FIGS. 4A and 4B, the bore 31 is formedin a central stem 51 of an umbrella 53 which forms part of the liner 1.In addition to the stem 51 at its centre, the umbrella 53 has a discportion 55 which extends outwards from the central stem 51 and which isembedded in the silicone of the liner 1. The disc portion 55 of theumbrella 53 includes a number of through holes 59 which are filled withsilicone and which help anchor the umbrella 53 within the silicone.

FIGS. 4A and 4B also show the perforations 23 which pass from theinterior surface 61 of the liner 1 to the outer face 11 of the end cap 7and which allow passage of air and sweat from the interior surface 61 toits exterior 11. The two perforations 23 which are shown in solid linesfall along the sectional line of these Figures and the perforations 23shown in broken lines are behind that sectional line. The socket 43 mayinclude a one-way expulsion valve (not shown), as is known in the art.Additionally or alternatively a vacuum device may be used to maintain areduced pressure within the socket 43.

When the sealing cap 3 is sandwiched between the distal end 9 of theliner 1 and the interior surface 63 of the socket, a gap 65 existsbetween the sealing cap 3 and the interior surface 63 of the socket 43.This gap 65 is as a result of the reduced thickness t_(O) of the skirt39O of the sealing cap 3 beyond the step 41. The gap 65 extends from thestep 41 to beyond a peripheral edge 67 of the sealing cap 3, such thatthe skirt 39O is able to move away from the outer face 11 of the end cap3 and into that gap 65. Since the skirt 39O is resiliently deformable,its “at rest” position is as shown in FIG. 4A, where it is in contactwith the outer face 11 of the end cap 7.

In use, when the residual limb 45 is surrounded by the liner 1 any sweatwhich is secreted from the skin of the amputee will cover the innersurface 61 of the liner and if left there can act as a lubricant,causing relative movement between the liner and residual limb, leadingto chafing and discomfort to the amputee. Since the liner 1 isperforated in the region of the end cap 7, any sweat, air or other fluidin that region is expelled through the perforations 23 when the residuallimb 45 loads the inner wall 61 of the liner 1. This loading occurswhilst the amputee is standing and during the stance phase of the gaitcycle when the residual limb 45 “pistons” within the liner 1. As sweatis forced though the perforations 23 it pushes against the inner surface33 of the sealing cap 3 in the region of the outer circumferential band39O of the frusto-conical portion 25 and this part of the skirt 39O willbe pushed away from the outer face 11 of the end cap and the skirt 39Omoves into the gap 65. The sweat makes its way over the peripheral edge67 of the sealing cap 3 and gathers in the gap 65, from where it maydrain out of the socket via the locking mechanism, or can be drawn awayvia a one way valve (if present), in either case optimally using anelevated vacuum source, such as a vacuum pump.

On completion of the stance phase of the gait cycle as the lower limblifts off the ground the residual limb 45 will have a tendency to bedrawn away from the interior surface 63 of the socket 43 in the regionof the end cap 7. During this phase of the gait cycle sweat will nolonger be pushed through the perforations 23 and due to the resiliencein the skirt 39O of the sealing cap 3 the interior wall 33 of thesealing cap 3 will return to its ‘at rest’ position and once again sealagainst the outer face 11 of the end cap 7. In addition oralternatively, the lifting of the residual limb 45 will cause a reducedpressure or partial vacuum in this region. This partial vacuum will betransmitted via the perforations 23 to the interior wall 33 of thesealing cap 3 and pull this against the outer face 11 of the end cap 7,thereby sealing the sealing cap 3 against the end cap 7. By sealing theend cap 7 in this manner the sealing cap 3 helps maintain a reducedpressure within the liner 1 which supports suspension of the liner 1 andthe rest of the prosthesis from the residual limb 45. In this manner,the combined action of the skirt 39O of the sealing cap 3 and the endcap 7 of the liner 1 function as a valve to maintain a reduced pressurewithin the cavity of the liner 1.

As the amputee continues to walk this process is repeated, with sweatbeing forced through the perforations 23 of the liner 1 during thestance phase when the distal end 9 of the liner 1 is compressed and withsealing cap 3 being drawn against the outer face 11 of the liner 1 toseal the liner 1 during the swing phase.

Various modifications will be apparent to those in the art and it isdesired to include all such modifications as fall within the scope ofthe accompanying claims.

For example, the body of the liner 1 in FIGS. 1-4B is made ofimpermeable silicone which is perforated at the distal end 21 of theliner 1. Whilst silicone is an impermeable material which in thoseFigures is perforated to make the liner 1 porous, instead of usingsilicone at the distal end 9 of the liner this part of the liner may bemade from a porous material, such as a sintered material or fabric suchas Gore-Tex®, which does not need to be perforated to allow passage ofair and moisture from the inside to the outside of the liner 1.

Since the displaceable skirt 39O of the sealing cap 3 is only incommunication with peripheral perforations 23 in the distal end 21 ofthe liner 1 (i.e., those which are distal to the centre 17 of the endcap 7) the perforations 23 which are proximal to the centre 17 of theend cap may, in practice, be permanently sealed, since the inner surface33 of the inner circumferential band 39I of the frusto-conical portion25 of the sealing cap 3 permanently abuts that portion of the end cap.This may lead to a build-up of moisture on the interior surface 61 ofthe liner 1 towards its axial centre. To address this situation an innerportion of the outer face 11 of the end cap 7 may be covered by a porousmembrane, such as a fabric layer. The fabric layer will act as awicking/transmission layer and allow sweat to be pushed from theinterior surface 61 of the liner 1, through the inner perforations 23and along the fabric layer to the peripheral edge 67 of the sealing cap3. In order to allow the sealing cap 3 to function as a valve by sealingagainst the outer face 11 of the end cap 7, an outer circumferentialband of the outer face 11 of the end cap 7 should be free from a porouscovering, so that when it is in contact with the corresponding part ofthe sealing cap 3 it provides a seal.

In the embodiments described above the sealing cap 3 is a separate piecefrom the locking liner. In other embodiments the sealing cap may bepermanently fixed to the distal end of the locking liner. For example,the sealing cap may be glued or otherwise bonded to the locking linerwhen the two parts are first mated. Alternatively the sealing cap may beintegrally formed on the end cap of the locking liner. If the sealingcap is fixed to the locking liner it would be joined in the region ofthe boss 15 of the liner so that the skirt 39O is free to move away fromand back towards the end face 11 of the locking liner 1, so as toprovide the valve functionality.

In the embodiment described above, the thickness of the sealing cap 3transitions from a thickness t_(i) of the inner circumferential band 39Iof the frusto-conical portion 25 to a thickness t_(O) of the outercircumferential band 39O of the frusto-conical portion 25, wheret_(i)>t_(O). In other embodiments the thickness of the frusto-conicalportion 25 may be constant as it extends outwards from the boss 27 or itmay decrease gently, without having a step 41. In such embodiments theability of the outer circumferential band 39O to move as a valve may beprovided by having a step in one or both of the end cap 7 of the liner 1and in the interior wall 63 of the socket, thereby defining a gap inwhich the outer circumferential band 39O may reciprocate.

Whilst the embodiment described with reference to the Figures uses alocking liner and locking pin, the invention can also be embodied in acushion (non-locking) liner. To achieve this the cushion liner andsealing cap will need to be adapted to locate the sealing cap on thedistal end of the liner in such a manner where lateral movement of theseparts is inhibited. Whilst the embodiment shown in the Figures uses aboss 15 on the liner and a cooperating recess 28 on the sealing cap 3,since a cushion liner does not typically include a boss, othermechanical interfaces can be used to locate the sealing cap on thedistal end of the cushion liner. These mechanical interfaces maycomprise a protrusion on one of the liner and the sealing cap and acooperating recess on the other of the liner and the sealing cap.Alternatively other locating means can be used such as hook and loopfastener, other mechanical engagements or magnets.

In the embodiment described above, the different thicknesses t_(i),t_(O) of the sealing cap 3 are provided by the inner circumferentialband 39I and the outer circumferential band 39O of the frusto-conicalportion 25. Since the function of the full thickness t_(i), portion isto bear the load of the amputee and the function of the reducedthickness t_(O) portion is to allow that portion of the sealing cap 3 tomove away from and back towards the end cap 7 of the liner 1, the fullthickness t_(i) portion and the reduced thickness t_(O) portion can bearranged other than concentrically. For example the outercircumferential band may be of full thickness and the innercircumferential band may be of a reduced thickness, so that the innercircumferential band moves away from and back towards the liner end cap7 during the gait cycle. According to this arrangement the innercircumferential band would include perforations or other holes or slitsto allow passage of sweat etc. from the interior surface 31 of thesealing cap 3 to the interior surface 61 of the socket 43. These holesor slits would not be aligned with the perforations 23 of the liner 1,so that the inner circumferential band will seal against the liner endcap 7 when abutted thereto. Alternatively the full thickness portionsmay be formed as radially extending spines with reduced thicknessportions therebetween.

The sealing cap 3 described above is disposed on the distal end 9 of theliner 1. In other embodiments a sealing cap or flap may be disposed at adifferent position of the liner 1 corresponding to a perforated portionof the liner 1. For example, if a side wall of the liner 1 is perforatedinstead of or in addition to the distal end 9 of the liner, the sealingcap would have a portion which is movable between a first position(where it is adapted to abut the perforated portion of the liner) and asecond position (where it adapted to be spaced from that portion of theliner) in accordance with the invention. As described above the sealingcap or flap may be a separate piece from the liner or permanentlyattached thereto.

In our earlier patent application published as US-A-2012/191218, thecontents of which are incorporated herein by reference, we describe avacuum-assisted suspension device for a lower limb prosthesis whichsecures the prosthesis to a residual body portion. FIG. 8D of thatpublication describes the use of voids 104V in a surface of a pad 104.The voids 104V are open to the surface 104O of the pad 104 and have ablind end in the body of the pad 104. The voids 104V assist inevacuating air from between the socket and the stump, as described inthat publication, when the pad 104 is repeatedly compressed. Similarlyvoids may be incorporated in one or both of the end cap 7 of theperforated liner 1 and the sealing cap 3, with the voids being open tothe outer face 11 of the end cap 7 and the interior surface 33 of thesealing cap respectively. Similarly, other voids as described in thatpublication can be used to enhance the vacuum between the end cap 7 andthe sealing cap 3.

What is claimed is:
 1. A prosthesis liner system comprising: a porousprosthesis liner, and a sealing cap, the porous prosthesis liner havinga perforated distal end, the perforated distal end including aperforated end cap having a plurality of perforations, the sealing capcomprising: a first portion comprising a protrusion on one of theperforated end cam or the sealing cap and a cooperating recess on theother of the perforated end cap or the sealing cap, to locate thesealing cap on the distal end of the porous prosthesis liner; and asecond portion having a proximal surface and an opposed distal surfaceand which is resiliently deformable and movable between: a firstposition where the proximal surface of the second portion is adapted toabut a corresponding portion of the perforated end cap, and a secondposition where the proximal surface of the second portion is adapted tobe spaced from said corresponding portion of the perforated end cap,wherein the second portion is a frusto-conical shaped skirt.
 2. Theprosthesis liner system as claimed in claim 1, wherein the perforatedend cap comprises a boss and the sealing cap comprises a cooperatingrecess.
 3. The prosthesis liner system as claimed in claim 1, whereinthe porous prosthesis liner is a locking liner comprising a bore, thesealing cap comprises an aperture adapted to be in communication withthe bore and the bore and aperture are adapted to receive a locking pinwhich is adapted to be fed through the aperture into the bore.
 4. Theprosthesis liner system as claimed in claim 1, wherein the first portioncomprises a frusto-conical part between the protrusion or recess and theskirt.
 5. The prosthesis liner system as claimed in claim 4, wherein thefrusto-conical part of the first portion has a thickness more than athickness of the skirt.
 6. A prosthesis suspension system, comprising: asocket for receiving a residual limb and including mounting means forbeing mounted to a prosthetic limb; and the prosthesis liner system asdefined in claim 1, the porous prosthesis liner having attachment meansfor attaching the porous prosthesis liner to the socket; and the sealingcap is adapted to be disposed between the porous prosthesis liner andthe socket, the system further comprising a gap between the skirt of thesealing cap and an interior wall of the socket in which the secondportion of the sealing cap is able to move between its first and secondpositions.
 7. The prosthesis suspension system as claimed in claim 6,wherein the attachment means for attaching the porous prosthesis linerto the socket is one or more of the group consisting of: a locking pin,a vacuum source, a seal between the porous prosthesis liner and thesocket, and a sleeve for sealing a proximal edge of the socket.
 8. Theprosthesis suspension system as claimed in claim 7, wherein the sockethas an expulsion port.
 9. The prosthesis suspension system as claimed inclaim 6, wherein the porous prosthesis liner has an outer wicking layerand the distal end of the porous prosthesis liner is perforated where itis in contact with the first portion of the sealing cap.